kem/hybrid: ensure X25519 hybrids fails with low order points #541
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
armfazh
reviewed
Mar 21, 2025
bwesterb
reviewed
Mar 21, 2025
bwesterb
approved these changes
Mar 21, 2025
|
This PR currently rejects bad cases after the ECDH calculation. This could also be fixed by rejecting public keys with low-order points in UnmarshalBinaryPublicKey, consistent with how bad cases for NIST curves are prevented. This could require a new Any particular preference? |
Lekensteyn
force-pushed
the
pwu/kem-check-low-order-x25519-point
branch
from
40a65c5 to
e315ae0
Compare
X25519 public keys with low order points result in an all-zeroes shared secret. Ensure that hybrids with X25519 and X448 fail during Encapsulate and Decapsulate when the peer provides such a garbage public key.
Lekensteyn
force-pushed
the
pwu/kem-check-low-order-x25519-point
branch
from
e315ae0 to
3f06680
Compare
You can't hit the case unless you try, so hitting the error late is not a problem. |
lukevalenta
approved these changes
Mar 21, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
X25519 public keys with low order points result in an all-zeroes shared secret. Ensure that hybrids with X25519 and X448 fail during Encapsulate and Decapsulate when the peer provides such a garbage public key.
I discovered this while rebasing our Go fork on Go 1.24 which upgraded the BoGo test suite as part of implementing X25519MLKEM768: golang/go@4b7f7cd#diff-db7320adf5b82005863ef324a30e91235d0268afe79856722226022f3afc2611
That upgrade pulled in this change that adds extra tests for key shares: google/boringssl@ed95627
Without this fix, these
crypto/tlstests would fail as the TLS handshake continues instead of aborting:I don't think this is a security issue, garbage in, garbage out. Nevertheless, it doesn't hurt to add the extra checks.